Hilton Head is actually home to 8 different Marriott Vacation Worldwide properties - just to make the more decision complicated for you!
I did talk to some folks at MVC, though, and tried to get the inside scoop. Here's exactly what I was told:
"The main thing people looking to reserve want to know is the resort’s location in reference to the Ocean. Grande Ocean, Barony Beach Club, SurfWatch and Monarch are ocean front properties with direct access to the beach (at SurfWatch you have to cross a short walkway over marsh to get to the beach). Harbour Pointe, Sunset Pointe, Harbour Club, and Heritage Club are not on the ocean, but have views of the water (via inlet, harbor, river, etc). Among guests, SurfWatch and Grande Ocean are the favorites. SurfWatch has the benefit of being a newer site while still being very close (walkway) to the beach. Grande Ocean has the best location and the most amenities available."
I hope this helps you. Since each property offers a variety of guest room types, family activities and recreational activities, it can get overwhelming. The best resource to research the benefits of each property individually is marriottvacationclub.com.